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Wednesday, May 14, 2014

14/05/14: Inbreeding and Disease in Tropical Shrimp Aquaculture: a Reappraisal and Caution

ENACA
strongly recommends that anyone involved in shrimp aquaculture - particularly
hatcheries but also anyone procuring PL - read the following paper which was
published in Aquaculture
Research.

The
disease crisis facing shrimp aquaculture may be propelled, in part, by an
interaction between management practices that cause inbreeding, and the
amplification by inbreeding of susceptibility to disease and environmental stresses. The study describes and numerically simulates gene flow from Penaeus
(Litopenaeus) vannamei hatcheries that employ a ‘Breeder Lock’ to
discourage use of their PL as breeders, through ‘copy hatcheries’ that breed
the locked PL, to inbred shrimp in farm ponds. Re-analysis of published data
shows that inbreeding depression under stress is exceptionally strong in
shrimp. Inbreeding is currently overlooked as a problem because: (1) procedures
recommended for well-managed hatcheries do not consider their implications for
the copy hatcheries that supply most farmed shrimp (estimated 70%), (2)
inbreeding in hatcheries is often reported as zero even though zero is the
mathematical expectation of the usual estimator (Fis, fixation index) whatever
the true genealogy of the broodstock. Simulation shows, however, that
inbreeding can be estimated with Wang's trioML estimator, that Fis can
differentiate Breeder Locked from copy PL and that simple tests can verify the
lock status of PL. The importance of inbreeding should be re-evaluated in the
context of disease and environmental stress. Unrecognized inbreeding may
increase the incidence, prevalence and lethality of WSSV, IHHNV, EMS (AHPND)
and other diseases.

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